Method for forming a hollow of a ferritic FeCrAl alloy into a tube

Abstract

The present invention relates to a method for forming a hollow 26 of a ferritic FeCrAl alloy into a tube 2. While tubes made of powder metallurgical, dispersion hardened, ferritic FeCrAl alloys are commercially available, hollows made of FeCrAl alloys so far can hardly be formed into tubes of small dimensions. The major reason for the problems in forming hollows of a ferritic FeCrAI alloy into a finished product is that FeCrAl alloys are brittle. It is therefore an aspect of the present invention to provide a tube 2 made of a ferritic FeCrAl alloy having arbitrary small dimensions. Furthermore, it is an aspect of the present invention to provide a machine 1 and a method for forming a tubular hollow 26 into a finished tube 2 of a ferritic FeCrAl alloy. At least one of the above aspects is addressed by a method for forming a hollow into a tube 2 comprising the steps providing the hollow 26 of a ferritic FeCrAl alloy, heating the hollow 26 to a temperature in a range from 90° C. to 150° C., and forming the heated hollow 26 by pilger milling or drawing into the tube.

The invention claimed is: 
     
       1. A method for forming a hollow into a tube, comprising the steps of:
 manufacturing a billet of a ferritic FeCrAl alloy by a powder metallurgical process; 
 forming a hollow from the billet of ferritic FeCrAl alloy; 
 heating the hollow to a temperature in a range from 90° C. to 150° C.; and 
 forming the heated hollow by pilger milling or drawing into the tube, wherein the tube has an outer diameter of 25 mm or less, and wherein the ferritic FeCrAl alloy comprises, in wt-%:
 Cr 9 to 25, 
 Al 3 to 7, 
 Mo 0 to 5, 
 C 0 to 0.08, 
 Si 0 to 3.0, 
 Mn 0 to 0.5, 
 balance Fe. 
 
 
     
     
       2. The method according to  claim 1 , wherein prior to the step of heating at least an outer surface of the hollow is coated with a polymer serving as a lubricant. 
     
     
       3. The method according to  claim 2 , wherein prior to the step of heating the hollow is coated with a polymer serving as a lubricant by immersing the hollow into a polymer suspension and drying of the hollow after immersion. 
     
     
       4. The method according to  claim 2 , wherein the hollow is blasted prior to the coating. 
     
     
       5. The method according to  claim 2 , wherein during the step of forming the hollow is drawn through a drawing die and over a mandrel, and wherein prior to the coating the hollow is blasted on an inner surface, only. 
     
     
       6. The method according to  claim 1 , wherein during the step of forming an oil based lubricant is applied onto the hollow. 
     
     
       7. The method according to  claim 6 , wherein during the step of forming the hollow is drawn through a drawing die and over a mandrel, and wherein the oil based lubricant is applied onto an outer surface of the hollow, only. 
     
     
       8. The method according to  claim 1 , wherein in the step of providing the hollow, the hollow is extruded from a billet. 
     
     
       9. The method according to  claim 1 , wherein the tube has an outer diameter of 10 mm or less. 
     
     
       10. The method according to  claim 1 , wherein the step of heating the hollow includes feeding the hollow through an induction coil in a longitudinal direction of the induction coil. 
     
     
       11. The method according to  claim 1 , wherein no further working of the hollow occurs between the step of heating the hollow to a temperature in a range from 90° C. to 150° C. and the step of forming the heated hollow by pilger milling or drawing into the tube. 
     
     
       12. A method according to  claim 6 , for forming a hollow into a tube, comprising the steps of:
 manufacturing a billet of a ferritic FeCrAl alloy by a powder metallurgical process; 
 forming a hollow from the billet of ferritic FeCrAl alloy; 
 heating the hollow to a temperature in a range from 90° C. to 150° C.; and 
 forming the heated hollow by pilger milling or drawing into the tube, wherein the tube has an outer diameter of 25 mm or less, and wherein the ferritic FeCrAl alloy comprises, in wt-%:
 Cr 9-25, 
 Al 3-7, 
 Mo 0-5, 
 Y 0.05-0.60, 
 Zr 0.01-0.30, 
 Hf 0.05-0.50, 
 Ta 0.05-0.50, 
 Ti 0-0.10, 
 C 0.01-0.05, 
 N 0.01-0.06, 
 O 0.02-0.10, 
 Si 0.10-3.0, 
 Mn 0.05-0.50, 
 P 0-0.8, 
 S 0-0.005, 
 balance Fe. 
 
 
     
     
       13. The method according to  claim 12 , wherein prior to the step of heating at least an outer surface of the hollow is coated with a polymer serving as a lubricant. 
     
     
       14. The method according to  claim 13 , wherein prior to the step of heating the hollow is coated with a polymer serving as a lubricant by immersing the hollow into a polymer suspension and drying of the hollow after immersion. 
     
     
       15. The method according to  claim 13 , wherein the hollow is blasted prior to the coating. 
     
     
       16. The method according to  claim 13 , wherein during the step of forming the hollow is drawn through a drawing die and over a mandrel, and wherein prior to the coating the hollow is blasted on an inner surface, only. 
     
     
       17. The method according to  claim 12 , wherein the tube has an outer diameter of 10 mm or less. 
     
     
       18. The method according to  claim 12 , wherein the step of heating the hollow includes feeding the hollow through an induction coil in a longitudinal direction of the induction coil. 
     
     
       19. The method according to  claim 12 , wherein no further working of the hollow occurs between the step of heating the hollow to a temperature in a range from 90° C. to 150° C. and the step of forming the heated hollow by pilger milling or drawing into the tube.